It is known to control hydraulic equipment such as excavators and the like using a resolved motion control systems wherein operator inputs controlling end point movement are applied to a computer system which computes, for example, by inverse kinematics or the like, the angular adjustments or movements of the joints and the speed of such adjustments or movements required to attain the desired end point movement and provides signals to control adjustment of the control valve for each actuator causing the actuator to adjust relationships of the elements controlled to obtain the desired end point movement.
Generally the control valve for each actuator is a spool valve that adjusts flow, for example, to a selected end of the double acting hydraulic actuator and permits flow of fluid from the unselected end of the actuator (to the tank).
It will be apparent that manipulating the control valve to obtain a desired movement of the actuator must also ensure that, in fact, the required movements of the various elements of the system (e.g. arm segments of an articulated arm) to move the end point to the desired location are taking place and at the required or desired rate. If the required movement is lagging behind the desired movement as commanded by the operator by too great a distance problems may be encountered and it has been found desirable to modify the instructions to the control valves when a discrepancy between the desired and actual end point position exceeds certain limits (see U.S. patent application Ser. No. 07/556,417 filed Jul. 24, 1990 Frenette et al).
It will further be apparent that the actual conditions or forces necessary to manipulate the arm and move the end point to the desired location may vary widely depending on, for example, the load being moved, i.e. the resistance (or lack thereof) to movement.